The present invention relates to hard disk drive systems having transducers including a magnetic core with a gap adjacent to a magnetic storage disk.
Hard disk drives have traditionally employed electromagnetic transducers that are spaced from a rapidly spinning rigid disk by a thin layer of air that moves with the disk surface. Such an air layer helps to avoid damage between the rapidly spinning disk and the essentially stationary transducer, which is constructed with a large, aerodynamic xe2x80x9csliderxe2x80x9d designed to xe2x80x9cflyxe2x80x9d over the surface, buoyed by the moving air layer. The air layer, however, creates an additional space between the transducer and the magnetic medium of the disk that is used to store information. This spacing lowers the density with which data can be stored and lowers the resolution and amplitude with which data can be retrieved.
Conventional flying heads have a pair of poletips formed by thin film processes on a back end of the slider and terminating coextensively with the slider air bearing surface. In flight, the slider is tipped so that the back end is lower than the front end and the poletips are closer to the disk than the remainder of the slider. Other flying heads, representative of which is U.S. Pat. No. 4,698,708 to Lazarri, have poletips that are flush with the air bearing surface of the slider partially between the front and back ends.
In an attempt to lower the spacing loss and thereby increase resolution and amplitude, transducer flying heights have generally decreased over many years in the magnetic recording industry. Lowering the flying height, however, encounters a countervailing problem of catastrophic head crash that occurs when the transducer impacts the rapidly spinning disk. In recent years a solution to the conflict between flying height and head crash has been achieved by designing the drive system so that the head supporting structure is run in continuous sliding contact with the disk, which can reduce the problem of impact between the head and disk and decrease the spacing between the head and disk. Any perturbation that causes separation between the head and disk, however, can result in a crash when the two recontact. Such a perturbation can be due to a shock to the drive, such as would occur from accidental bumping of the drive or its support, or can be due to the presence on the disk surface of an asperity or debris. Note that in either situation, a potentially destructive impact can occur due to the initial perturbation, instead of or in addition to the crash upon recontact.
In U.S. Pat. No. 5,041,932, Hamilton discloses a transducer that operates in contact with a rigid disk surface without destructive head crash, essentially by designing the mechanical and inertial characteristics of the transducer to conform to the rapidly spinning rigid disk without damage to the disk or transducer. A different approach for a hard disk drive system for allowing operational contact between the head and the disk is disclosed in U.S. Pat. No. 4,819,091 to Brezoczky et al., which proposes that nondestructive wear may be possible provided that the slider material is so much more thermally conductive than the disk that the slider surface is maintained at a lower temperature than the much larger disk surface as the slider rubs on the disk. And U.S. Pat. No. 4,901,185 to Kubo et al. teaches operational contact between a disk and a slider having a head appended and spaced from contacting the disk to avoid damage to the head. More recently, U.S. Pat. No. 5,327,310 to Bischoff et al. teaches a transducer similar to that disclosed in the Hamilton patent but having a ring-shaped transducer mounted vertically on a trailing end of a slider that makes intermittent, bouncing contact (xe2x80x9cpseudo-contactxe2x80x9d) with the disk.
An object of the present invention is to provide a transducer optimized for minimal head-medium spacing during longitudinal recording on and reading from the medium. A related object is for such a transducer to be stable and biased toward contact with a disk surface without the need for excessive force to hold the transducer to the surface against the lifting force of an air layer that moves with the disk, thereby avoiding problems of vibration and damage to the disk and/or transducer. In concert with the above objects it is desired to provide a transducer having efficient electromagnetic signal transduction.
The above objects are achieved with a transducer shaped like a low-profile table with three short support legs that slide on the medium surface during information transfer between the transducer and the medium. The transducer includes a magnetic core which stretches like a shallow, symmetric loop within the plane of the table, with ends of the loop extending into one of the legs to form a pair of closely spaced magnetic poletips exposed to the disk surfacein close proximity to the medium. Inductively coupled to the core is a conductive coil that spirals in opposite directions around laterally opposed sections of the core, the spirals stacked like pancakes centered on the opposed core sections. The core and the coil extend substantially further in the plane of the table top than along the direction with which the legs project, affording the mechanically and aerodynamically favorable low profile shape. The table top may be T-shaped or trapezoidal, reducing the mass of the transducer and increasing the number of transducers that can be obtained per wafer while retaining three-legged stability.
During writing of information to the medium, a current in the coil creates a magnetic field along the length of the loop shaped core, creating a magnetic field that spans the microscopic gap between the ends of the core and induces a similarly directed magnetic field in the adjacent media layer. Since the poletips are in contact with the disk surface and have an extremely small gap, very high resolution writing of information can be accomplished with this system. Unlike conventional heads which have tight tolerances for vertical throat height, the dimensions of the planar core of the present invention allow the throat height to vary substantially without impeding writing and reading efficiency, affording tolerance for wear of the sliding poletips. Additionally, the planar core allows the head to assume a relatively flat, stable, low-profile conformation with lower moment arms about the head-disk contact area, including both a lower moment of inertia of the chip and a lower effective mounting point of the beam holding the chip.
Reading of magnetic patterns imbued in the medium occurs due to the changing magnetic field seen by the poletips from the spinning disk on which the tips slide, creating a voltage in the inductively coupled coil that is read as a signal. Due to the intimate contact between the poletips and the recording surface, very high signal resolution and amplitude is achieved. In order to increase the high frequency permeance of the head, the core is formed of elongated strips, layers or filaments. Additionally, the poletips may be coated with a high magnetic saturation material adjacent to the gap in order to provide an intense magnetic field across the gap without saturation, even at field strengths of up to and exceeding 10,000 Gauss. In a preferred embodiment, the core is shaped like a clamshell, allowing formation of several coil layers within the core without unnecessarily increasing the reluctance of the core.
The low-profile, three-legged transducer is attached via a gimbal to a load beam to present a dynamic configuration that closely and rapidly conforms to a spinning disk so as to maintain contact and high resolution communication with the medium. Due to the small legs, which act like short stilts lifting the rest of the transducer above the thin moving air layer that adjoins the disk, little of the transducer is impinged upon by that thin moving air layer, and so minimal lifting force is generated that must be overcome to maintain contact. The interconnection between the transducer and the gimbal is made with exposed conductive bumps that pierce and are anchored to an outer insulative layer of the transducer, providing mechanical as well as electrical connections. The transducer is built in layers, along with many other transducers, on the surface of a wafer substrate from which the transducers are later removed, allowing the transducer to be much smaller and lighter in weight than conventional transducers that include bulk substrate materials. The legs, including the magnetically active leg containing the projecting poletips, are formed last, allowing careful tailoring of the most sensitive portions of the transducer.